Detector for physiological quantities

ABSTRACT

A device for detecting physiological quantities, comprising two hinged arms which are provided on their end with freely movable end members. When a part of the body, for example, an ear lobe, is clamped between the end members, the latter will be immovably retained in a mount.

limited States atent 1 1 Van Nie May 14, 1974 DETECTOR FOR PHYSIOLOGICALQUANTITIES [56] References Cited- [75] Inventor: Cornelis Pieter VanNie, UNITED STATES PATENTS Emmasingel, Netherlands 3,152,587 10/1964Ullrich et al. 128/2 L 3,006,673 10/1961 Swick 2 8/1888 [73] Asslgneei'P cmlmramn New 3,227,155 1/1966 Erickson et al. 128/2 L Y NY 3,628,52512/1971 Polany et al. 128/2 L Filed, Oct 13 1972 1,358,640 11/1920Kayama 248/182 [21] Appl. No.: 297,243 Primary ExaminerWilliam E. KammAttorney, Agent, or Firm-Frank R. Trifari [30] Foreign ApplicationPriority Data 71 14606 ABSTRACT l' 1971 Netherlands A device fordetecting physiological quantities, comprising two hinged arms which areprovided on their 1 128/205 end with freely movable end members. When apart of Int Cl 1 5/02 the body, for example, an ear lobe, is clamped be-[58] Fieid E 2.05 P tween the end members, the latter will be immovablyretained in a mount 10 Claims, 11 DrawingFigures PATENTEDHAY 14 I974SHEET 2 0f 2 Fig.7

1 to each other by a hinge near one end, each arm accommodating an endmember near its free end, at least one of the end members beingdisplaceable with respect to the associated arm, it being possible tohold a part of a body such as an earlobe or a finger tip between saidend members, at least one of said end members comprising a measuringhead.

A detector of this kind is known from US. Pat. No. 3,l52,587 and isoften used for measuring, for example, the blood pressure or the heartfrequency of patients, in particular patients whose life is in danger,such as after major surgery. It is then of essential importance that allrelevant signals generated by the body are detected by the detector,whilst the detector itself should not cause any interference signals.

For example, when the heart frequency is measured use is often made of adetector which comprises a lamp and a photosensitive element betweenwhich an earlobe of the patient is placed so that the light produced bythe lamp passes through the earlobe before it impinges upon thephotosensitive element. Any variation of the quantity of blood in theearlobe due to the heart beat will change the amount of lighttransmitted through the ear lobe, which results in a variation of thesignal produced by the photosensitive element.

Variations in the quantity of light received by the element occur alsoif the detector is displaced over the earlobe or if the distance betweenthe lamp and the element changes. These variations also lead to signalvariations (so-termed movement artefacts) which the measuring apparatusconnected to the element generally cannot distinguish from signalvariations which are caused by the heart beat.

The invention has for its object to provide a construction by which theoccurrence of such disturbing signals is substantially avoided. To thisend, a detector according to the invention is characterized in that thefree end of at least one of the arms is provided with a mount, theshape, the dimensions and the nature of the surface of the mount and ofthe surface of the associated end member which faces the mount and whichis connected to the arm via a flexible connecting member being chosensuch that the end member is arranged to be immovable in the mount whenthe end member is subjected to a force engaging the vicinity of itscentre and acting in the direction of the mount.

Consequently, the end members are freely movable with respect to thearms while the detector is being arranged on the part of the body sothat optimum adjustment of the end members to the contours of this bodypart is possible, whilst after the detector has been mounted the endmembers are unmovably held in their mount so that they can no longermove. with respect to each other and movement artefacts are hardlypossible.

A construction which was found to be very satisfactory is characterizedin that the mount comprises a rotation-symmetrical recess in the arm,the shape of they surface of the end member which faces the mount havinga rotation-symmetry which is adapted to the shape of the said recess.The surface of the end member which faces the mount is preferablyspherical, the mount being annular and comprising three bearing pointsfor the spherical surface which are regularly distributed over itscircumference.

The flexible connecting member which is used for connecting the endmember to the arm is preferably formed by an e-shaped resilient wire,the straight portion of which is located to be rotatable in the endmember near the centre of the surface facing the mount, the bent portionbeing arranged in a groove which is recessed in the arm.

So as to press the end members sufficiently rigidly into the mounts, thepressing force must exceed a given minimum value. On the other hand,this force should not be too large as this will bother the patient,particularly in the case of prolonged use of the detector. A frequentlyoccurring complaint associated with the use of the detectors known thusfar is, for example, a pronounced irritation of the skin at the areaswhere the detector presses against the body part. Furthermore, it shouldbe avoided that any accidental touching of the detectorfcauses movementartefacts due to the variation of the angle between the arms.Consequently, a given rigidity of the detector is required, at leastafter it has been arranged on the relevant part of the body. Such arigidity is achieved for the detector described in the said U.S. PatentSpecification in that a screw must be turned for changing the anglebetween the arms. However, this is cumbersome and, in addition, theevaluation of the pressing force is difficult.

An embodiment of the detector according to the invention whicheliminates these drawbacks while maintaining the advantages, ischaracterized in that the force to be exerted at the area of the centreof the end members in order to hinge the arms with respect to each otheris composed of a combination of a force which is produced by a clampingspring and a frictionalthe hinge in that the hinge pin is also insertedthroughat least one friction ring which is arranged between two eyelets,the friction pack formed by the eyelets and the friction rings beingcompressed in the axial direction by a'compression spring.

The force exerted by the compression spring is preferably made to beadjustable so as to enable adjustment of the friction.

After the detector has been arranged on the body part, it can sometimeshappen that the detector'is displaced by external forces which are largecompared to the force exerted by the combination of the clamping springand the friction. Such forces occur, for example, when the detector isjolted. So as to prevent this kind of displacement, a variant of thedetector according to the invention is characterized in that part of thehinge pin is formed by a screw bolt which cooperates with a nut which,by tightening, can exert a compressive force in the axial direction onthe friction pack, the said force being substantially larger than theforce exerted by the compression spring.

The invention will be described ence to the drawings.

FIG. I is a perspective view of an embodiment of a detector according tothe invention,

FlG. 2 shows how an end member of the detector shown in FIG. 1 isconnected,

in detail with refer- FIG. 3 shows a mount of the same detector,

FIGS. 4, 5 and 6 illustrate how the end member ofthe detector can beunmovably held in the mount by a force exerted thereon,

FIGS. 7 and 8 are sectional views of two embodiments of a hinge for adetector according to the invention,

FIG. 9 is a perspective view of an end member and an associatedmeasuring head for a detector according to the invention,

FIG. 10 shows an embodiment of such a measuring head, and

FIG. 11 illustrates. how the detector according to FIG. 1 can be used.

The detector 1 for physiological quantities which is shown in FIG. 1comprises two arms 3 which are connected to each other near one of theirends by a hinge 5. Near their free end, each of the arms 3 accommodatesan end member 7 which comprises a measuring head 9. Between the two endmembers 7 a body part such as an ear lobe or a tip of a finger can beheld, the measuring heads 9 then contacting the skin. So as tofacilitate the arrangement of the detector on the body part each of thearms 3 is extended beyond the hinge 5 by an end portion 11 which isadapted to the shape of the fingers.

Each of the arms 3 is provided with an annular mount 13 which comprisesa rotation-symmetrical recess 14 in the arm 3'. The end members 7 areconnected to the arms 3 in a floating manner so that they have a limitedfreedom of movement in all directions. However, if an end member 7 issubjected to a force engaging near its .centre and acting in thedirection of the associated mount 13, the end member will be unmovablylocated in the mount. These properties are due to a proper choice of theshape, the dimensions and the materials of the mount and of the surfaceof the end member which faces the mount; this will be describedhereinafter with reference to the FIGS. 4 to 6.

FIG. 4 is a cross-sectional view of a semi-cylindrical body 15 which isarranged in a trough 17 such that it bears on the edges 19 on thetrough. lfa force F acting in the direction of the trough 17 is exertedon the body 15 at the area of a point P, the body will be subjected atthe area of the edges 19 of the trough both to normal forces andfrictional forces. The normal forces, denoted in FIG. 4 by N, and N areper definition directed perpendicular to the surface of the body 15 andhence in the direction of the centre M of the section. The frictionalforces W and W are parallel to the said surface and their directionopposes that in which the body I5 could start to rotate as a result ofthe force F. The maximum value of the frictional force is dependent ofthe value of the associated normal force and of the frictioncoefficientfwhich is determined by the material properties of the bodyI5 and the trough edges 19. This dependency is given by the formula W=fN. The resultant of the forces W and N acts along a load line whichencloses an angle p. (called friction angle) with g the direction of thenormal force N. It will be obvious that on the basis of the foregoingformula tg' pt =f. This means that p. is independent of the value of theforce F. The load lines for the forces at the area of the two troughedges 19 are denoted in FIG. 4 by I, and I They intersect each other ina point 5,, the projection on the upper surface of the body I5 of whichis denoted by S,.

Considering the foregoing, the location of S, and S, is also independentof the value of F.

Analogous reasoning can be followed for a force F which engages on theright of M. In that case a second intersection is found which is denotedin FIG. 4 by S the projection thereof on the upper surface of the body15 being denoted by S;. The location of the point of application P withrespect to 5' and S: is decisive for the question whether or not thebody 15 will be stable in the trough 17. If? lies between S, and 8' thebody 15 cannot be brought to rotation by the force F. regardless of thevalue of, F. In a plan view, this stable" area has the form of a bandwhich extends in the longitudinal direction of the body 15 on both sidesof the axis thereof (see the shaded area in FIG. 5). A force which isdirected towards the trough l7 and which engages outside this area willbring the body to rotation.

It will be obvious that the width of the shaded area in FIG. 5 isdependent only of the diameter of the body 15, the width of the troughl7 and the friction coefficientf. If the friction coefficientsfat thearea of the lefthand and the right-hand trough edge I9 are not the same,the two angles ,u. will be different and the shaded area will beasymmetrical with respect to the axisof the body 15.

The requirement that the end member must be unmovably pressed into themount by a force which is exerted thereon and which acts in thedirection of the mount can thus be satisfied by choosing an end memberin the form of a semi-cylinder and a mount which comprises two troughedges. However, the position of the end members can be even betteradapted to the surface of the part of the body if the mount 13 isannular (see FIG. 3) and the surface of the end member 7 which faces themount is spherical. It is to be noted that the mount must comprise threebearing points 21 for the spherical surface which are preferablyregularly distributed over its circumference. If this is not the case,it can hardly be prevented that, due to manufacturing tolerances, theend member 7 contacts the mount 13 only at two locations, so that theend member can wobble in the mount.

For the combination of an annular mount 13 with three bearing points 21and an end member 7 having a spherical surface it is also possible tocalculate an area on the end member within which a force acting in thedirection of the mount 13 must engage so as to keep the end memberunmovably in the mount. The twodimensional model shown in FIG. 4,hwoever, cannot be used due to the presence of three separate bearingpoints 21. The very complex three-dimensional calculation which would inthis case be required has been omitted for the sake of simplicity. Thestable area on the surface of the end member 7 which is remote from themount 13 which can be found by means of such a calculation or by a muchsimpler experimental determination, is denoted by a shaded area in FIG.6. The locations where this area is nearest to the edge of the endmember 7 correspond to the locations of the bearing points 21. The shapeand the extension of the area are dependent of the diameters of the endmember and the mount and of the friction coefficient at the area of thebearing point 21. Because the detector is generally used only on partsof the body which are readily deformed, the force exerted on the endmember 7 by the body part is usually regularly distributed over thesurface of the end member which is in contact with the body part. Thismeans that the resultant force usually engages near the centre of thissurface so that a stable area whose edge is nowhere nearer to the centreof the surface than one fourth of the radius of the circle limiting thesurface is generally sufliciently large to keep the end member 7unmovably retained in the mount 13 in all practical cases.

The floating attachment of the end member 7 to the arm 3 can be realizedin various manners by means of a flexible connecting member. Such aconnecting member can consist of, for example, three or more wires orbands which extend from the centre of the spherical surface to themount. However, a very simple and 'effective flexible connecting memberconsists of an eshaped resilient wire 23 made of, for example, springsteel, the straight portion of which protrudes through an aperture 25 inthe end member 7 with some clearance so that it is located to berotatable. The bent portion of the wire 23 lies in a groove 27 which isrecessed in the arm 3 and which is coaxial with the mount 13. Owing tothis connection the end member 7can perform the following movements: atilting movement in the plane perpendicular to the straight portion ofthe a wire 23 in that the end member hinges about this straight portion;a tilting movement perpendicular to the former tilting movement in thatthe straight portion and the adjoining bent portion of the wire aredeflected in a resilient manner; and a movement in the direction of theaxis of the mount in which case the wire is also the end member in thedirection of the mount must ex-.

ceed a given minimum value. This minimum value was found to be grammesin practice. On the other hand, the said force should not be too high asotherwise it will be annoying to the patient. It was found that in theinterest of the patient a maximum value of I00 grammes must be adheredto. Furthermore, movements of the arms 3 with respect to each othercause false'signals (movement artefacts), so that from this point ofview a completed rigid detector would be desirable.

In the detector shown in FIG. 1 the force exerted during opening andclosing at the area of the centre of the end members 7 is determined bya clamping spring 29 and by the friction in-the hinge 5. For eachhinging movement the friction of the hinge 5 must then be overcome. Whenthe detector is opened, this frictional force and the force of thespring 29 cooperate; the two forces oppose each other when the detectoris closed. By an appropriate choice of the resilience and the frictionalforce a suitable compromise can be reached between the threeabove-mentioned requirements. A suitable choice is, for example, thecase where the force produced by the clamping spring 29 at the area ofthe centre of the end members 7 amounts to approximately 50 grammes,whilst at the same areas a force of at least 1. ra tn frablapproximately 30 rammes! must be exerted so as to overcome the frictioninfthe hinge 5. During opening the force then amounts to 80 grammeswhilst it amounts to grammes during closing.

Each of the arms 3 comprises two eyelets 31 through which a hinge pin 33is inserted. Between two eyelets 31 .(forming part of different arms 3)a number (three in the case shown in FIG. 7) of friction rings 35 isprovided. The friction pack formed by the twov eyelets 31 and thefriction rings 35 is compressed in the axial direction by a helicalcompression spring 37 which is slid about the hinge pin. The forceexerted by the compression spring 37 can be adjusted by varying thethickness of the stack of friction rings 35. To this end, the hinge pin33 is provided with a head 39 at only one end, so that it can be readilypulled out of the eyelets 31. The two arms 3 are then separated andfriction rings 35 can be removed or added as desired. I

The value of the friction is not only determined by the force of thecompression spring 37, but also by thematerial properties of the eyelets31 and the friction rings 35. The eyelets 31 are preferably moulded,integral with the arms 3, of a suitable synthetic resin material, forexample, polycarbonate. The friction rings can be made of hard-paper orofa synthetic resin material which is filled with asbestos:

. A variant of the hinge shown in FIG. 7'is shown in FIG. 8. In thiscase a portion 41 of the hinge pin 33 is formed by a screw bolt whichcooperates with a nut 43. The screw bolt 41 is centered in the frictionpack 31, 35 by means of a bush 44. The nut 43 and the end of the hingepin 33 which is opposite to the screw bolt 41 are provided with aknurled head so that the nut can be readily tightened by hand, Thetightening of the nut 43 causes compression of the friction pack 31, 35in the axial direction between a locking ring 45 and a clamping plate47. This compressive force is substantially larger than the forceexerted in the same direction by the compression spring 37, so that thefriction caused by the tightening of the nut 43 also becomes very large.

As a result, the arms 3 are rigidly connected to each other as if itwere. Due to the tightening of the nut 43 after the'detector 1 has beenarranged on the body part, the distance between the arms 3 existing atthat instant is fixed so that the detector is rendered substan tiallyless sensitive to touching and movements of the patient. This isparticularly useful in the case of patients who are subjected tomeasurements during prolonged periods of time.

The measuring head 9 is preferably mounted to be detachable in the endmember 7. An example of such a construction is shown in FIG. 9. Themeasuring head 9 has the shape of a flat cylinder comprising aconnecting piece 49 which is connected to the cylinder wall and whichextends into a connecting cable 51. The cylindrical measuring head 9fits in a cylindricalcavity 53 which is recessed in the end member 7 andwhich communicates with the edgeof the end member 7 via a number (two inFIG. 9) of radial ducts 55 which can accommodate the connecting piece49. The connecting piece 49 is preferably made of a somewhat elasticsynthetic resin material and its dimensions are such that it has a tightfit in the radial duct 55. As a result, the measuring head 9 can berigidly secured and still be readily detachable in the end member 7. Thedirection of the connecting cable 51 with respect to the axis of theopening 25 is determined by the choice of theradial duct 55 in which theconnecting piece 49 is inserted. It is to be ensured that the chosendirection involves, in view of the arrangement of the detector on thebody, an as small as possible risk of movement artefacts due to touchingof the connecting cable 51.

In accordance with the desired measurements, the measuring head 9 cancomprise, for example, mechanical, optical or electrical measuringelements. A frequently applied measurement is the measurement of theheart frequency by optical measurement of periodic variations of thequantity of blood in a finger tip of ear lobe. As already described, oneof the two measuring heads 9 then usually comprises a lamp and the otherelement comprises a photosensitive element. If the lamp or thephotosensitive element become defective, measuring becomes impossibleuntil the defective measuring head has been replaced. If uninterruptedsupervision of the patient is required such as, for example, duringmajor surgery, this can be very dangerous. Consequently, in eachdetector 9 a lamp 57 and a photosensitive element 59 are preferablyarranged adjacent to each other (see FIG. 10). lfa defect occurs, themeasurement can be simply continued-by switching over. The replacementof the measuring head 9 can then be postponed until a suitable time, ifnecessary. If

desired, switching over can even be effected fully auto- .matically by.the measuring equipment used. The lamp 57 can be formed by alight-emissive diode and the photo-sensitive element 59 by aphotosensitive diode.

FIG. ll shows how the detector can be used in practice. The detector 1is connected to an ear lobe and the connecting cable 51 is attached-tothe neck of the patient with an adhesive tape 61 so that movements ofthe connecting cable are not transferred to the detector. If the patientlies in bed and must carry the detector 1 during a prolonged period oftime, it is desirable to prevent the patient from lyingon the detectorso that the detector would be jammed. This would give rise to subof asoft and rigid material, for example silicone rubber, is provided aboutthe ear to which the detector 1 is connected. The ring 63 is attached tothe head of the patient by means of adhesive tape 65.

What is claimed is: v

l. A device -for detecting physiological quantities comprising first andsecond arms connected to each other for pivotal movement of one withrespect to the stantial movement artefacts and could, moreover, be verypainful to the patient. Therefore, a thick ring 63 said mounting meansand in the vicinity of the center of said end member and at least one ofsaid end members is displaceable with respect to its associated arm whenno forces are applied thereto, flexible connecting means connecting saidend member to said mounting means, and measuring means carried by atleast one of said end members so as to detect said physiologicalquantities.

2. The device according to claim 1 wherein said recess isrotation-symmetrical and wherein the shape of the end member accomodatedwithin said recess has a rotation-symmetry adapted to the shape of 'saidrecess.

stantially at the center thereof near the surface facing said mountingmeans so as to be rotatable therewith, the bent portion of said e-shapedwire being arranged within said groove.

5. The device according to claim 1 further comprising a clamping springand wherein the force required to move said arms with respect to eachother is equal to the combination of the force produced by said clampingspring and a frictional force of said hinge, said frictional force beingat least 10 grams.

6'. The device according to claim 5 wherein said hinge comprises a hingepin inserted through eyelets on both arms, at least one friction ringarranged between two eyelets of one of said arms forming a friction packwith said eyelets, and a compression spring carried by said pin forexerting a compression force on said friction pack.

7. The device according to claim 6 further comprising a means foradjusting said compression force exerted by said spring carried on saidpin.

8. The device according to claim 6 further compris- I ing a screw boltextending axially through said pin and a nut for cooperative engagementtherewith, whereby rotational movement of said nut produces compressiveforces exerted in the axial direction on said friction pack, saidcompressive forces being substantially larger each other on each of saidend members.

1. A device for detecting physiological quantities comprising first andsecond arms connected to each other for pivotal movement of one withrespect to the other, a hinge located at one end of said arms forpivotally connecting said arms together, an end member carried on thefree end of each arm so as to locate therebetween a part of a body suchas an ear lobe or fingertip, a mounting means carried at the free end ofat least one of said arms comprising a recess in said arm for carryingits respective end member whereby said end member is immovablyaccomodated in said recess when a force is applied to said end member inthe direction of said mounting means and in the vicinity of the centerof said end member and at least one of said end members is displaceablewith respect to its associated arm when no forces are applied thereto,flexible connecting means connecting said end member to said mountingmeans, and measuring means carried by at least one of said end membersso as to detect said physiological quantities.
 2. The device accordingto claim 1 wherein said recess is rotation-symmetrical and wherein theshape of the end member accomodated within said recess has arotation-symmetry adapted to the shape of said recess.
 3. The detectoraccording to claim 2 wherein the surface of said end member facing itsrespective mounting means is spherical, and wherein said mounting meansis annular having three bearing points for supporting said sphericalsurface, said bearing points being evenly distributed about thecircumferance of said mounting means.
 4. The device according to claim 1further comprising a groove in the recess of at least one of said arms,and wherein said flexible connecting means comprises an e-shapedresilient wire, the straight portion of said e-shaped wire being locatedin said end member substantially at the center thereof near the surfacefacing said mounting means so as to be rotatable therewith, the bentportion of said e-shaped wire being arranged within said groove.
 5. Thedevice according to claim 1 further comprising a clamping spring andwherein the force required to move said arms with respect to each otheris equal to the combination of the force produced by said clampingspring and a frictional force of said hinge, said frictional force beingat least 10 grams.
 6. The device according to claim 5 wherein said hingecomprises a hinge pin inserted through eyelets on both arms, at leastone friction ring arranged between two eyelets of one of said armsforming a friction pack with said eyelets, and a compression springcarried by said pin for exerting a compression force on said frictionpack.
 7. The device according to claim 6 further comprising a means foradjusting said compression force exerted by said spring carried on saidpin.
 8. The device according to claim 6 further comprising a screw boltextending axially through said pin and a nut for cooperative engagementtherewith, whereby rotational movement of said nut produces compressiveforces exerted in the axial direction on said friction pack, saidcompressive forces being substantially larger than the force exerted bysaid compression spring.
 9. The device according to claim 1 wherein saidmeasuring means is detachably connected to said end members.
 10. Thedevice according to claim 1 wherein said measuring means furthercomprises a photo emissive means and a photosensitive means arrangedadjacent each other on each of said end members.